The present invention relates to a night vision system for detecting objects at relatively low visible light levels. In particular, the invention concerns an active night vision system having an anti-blinding scheme employing pulsed illumination and synchronization with detected pulsed light sources from oncoming vehicles.
Night vision systems are utilized to allow a user to see objects at relatively low visibility light levels. Night vision systems typically are classified as either passive night vision systems or active night vision systems. In known passive night vision systems used in automotive applications, mid-infrared cameras are used to image objects using the ambient infrared light emitted by the objects in the environment. Mid-infrared night vision systems have relatively few pixels and, accordingly, images formed using such cameras have low video resolution and a relatively narrow field of view. Known active night vision systems utilize a near-infrared (NIR) laser diode or a filtered incandescent light source to generate NIR light. The NIR light is subsequently reflected off objects in the environment and is received by a NIR-sensitive camera. The camera generates a video signal responsive to received light.
An improved active night vision system is disclosed in U.S. patent application Ser. No. 09/598,484 entitled xe2x80x9cA Night Vision System Utilizing A Diode Laser Illumination Module And A Method Related Thereto,xe2x80x9d which is herein incorporated by reference. That application describes an active night vision system that uses a NIR diode laser to illuminate the region forward of the vehicle, and a CCD camera to process and display images within the illuminated region. Because NIR light is invisible to the human eye, the laser light can be formed into a high beam pattern to illuminate potential hazards without blinding oncoming vehicle operators. Such systems, however, are susceptible to blinding by oncoming vehicles similarly equipped with a night vision NIR light source.
One solution to night vision system blinding by oncoming vehicles similarly equipped with a NIR light source is provided in U.S. patent application Ser. No. 09/683,840 entitled xe2x80x9cGPS-Based Anti-Blinding System For Active Night Vision.xe2x80x9d In that application, GPS is used to determine the direction of travel of the vehicles as well as an absolute time reference. Vehicles proximate one another synchronize their pulsed light sources to the absolute time reference signal with the phase of the light pulse based on the direction of motion of the respective vehicles. In this way, two cars approaching one another from opposite directions will have their NIR light sources pulsed out-of-phase with each other at duty cycles below 50% to avoid having their light source xe2x80x9conxe2x80x9d when the opposing vehicle""s camera is also xe2x80x9con.xe2x80x9d The disclosed anti-blinding scheme, however, requires that all night vision equipped vehicles must also be equipped with GPS systems.
Thus, there exists a need for alternate night vision systems and methods related thereto that mitigate or eliminate blinding of the vehicle""s night vision system by similarly equipped approaching vehicles.
The present invention provides an active night vision system and method related thereto which mitigates the blinding effects of nearby similarly equipped vehicles. The anti-blinding scheme of the present invention synchronizes the pulsed light sources of respective vehicles approaching each other from opposite directions to be out-of-phase without the use of GPS or any other external reference source. A night vision system in accordance with one embodiment of the present invention includes an illuminating device such as a NIR light source and beam-forming optics for illuminating a region in the forward direction of travel of the vehicle. A receiver, such as a camera, receives light reflected off objects in the illuminated region and generates a video signal responsive to the received light. A second light source is provided which acts as a timing trigger pulse operating at a wavelength different than the NIR light source. The light sensor is configured to detect light at a wavelength corresponding to the second light source and generate a timing signal in response thereto. The pulse timing of the second light source is known with respect to the first light source. Upon detecting another vehicle""s trigger light source, the controller adjusts the pulse phase of the first light source to be exactly out-of-phase with that of the oncoming vehicle since the pulsed timing of the oncoming vehicle""s NIR light source is known upon detection of the opposing vehicle""s trigger light source. In this way, the trigger light pulses are used to indicate the pulse timing of each respective vehicle""s primary NIR light source. By knowing the other vehicle""s light source timing sequence, the reference vehicle""s light source timing sequence can be adjusted accordingly to be out-of-phase and thus, non-interfering.
In another embodiment, a rearward trigger pulse is also emitted which differs from the forward trigger pulse or primary NIR pulse. The rearward trigger pulse is used to synchronize all vehicles traveling in the same direction in-phase, such that none are xe2x80x9cvisiblexe2x80x9d to the oncoming night-vision-equipped vehicles.
Other advantages and features of the invention will become apparent to one of skill in the art upon reading the following detailed description with reference to the drawings illustrating features of the invention by way of example.